ethdev: add outer IP checksum capability flag
ethdev: add outer IP checksum capability flag

If the flag is advertised by a PMD, the NIC supports the outer IP
checksum TX offload of tunneling packets, therefore an application can
set the PKT_TX_OUTER_IP_CKSUM flag in mbufs when transmitting on this
port.

Signed-off-by: Jijiang Liu <10b95deab7df654d0c21c8c98b54c9a1ecf2a5c0@intel.com>
Acked-by: Olivier Matz <dfcc1510895413197abb4336e39bb0a3906cba71@6wind.com>

john-mcnamara-intel/dpdk,venkynv/dpdk-mirror,msune/dpdk,tsphillips/dpdk-fork,tsphillips/dpdk-fork,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,tsphillips/dpdk-fork,venkynv/dpdk-mirror,mixja/dpdk,mixja/dpdk,msune/dpdk,venkynv/dpdk-mirror,tsphillips/dpdk-fork,mixja/dpdk,msune/dpdk,mixja/dpdk,msune/dpdk,venkynv/dpdk-mirror,john-mcnamara-intel/dpdk